This invention relates generally to a knowledge system and more particularly to a knowledge system for determining the environmental performance of specific chemical controlled release devices, the effects of combinations of polymers and carriers on the release rate from the device, and the characteristics of the controlled release device that will meet specified design performance characteristics.
Methods for controlling plant root growth into below ground repositories containing buried nuclear and chemical wastes, insect intrusion into Wood structures, fungal attack on Wood structures, and rodent intrusion into food storage and shipping containers have been subjects of recent research. While a number of chemicals are available for controlling plant, fungi, insect, and rodent intrusion, concerns have been raised about the safety of current technologies with regard to both human health and safety and potential impacts to the environment. Furthermore, chemicals must be applied repeatedly to provide effectiveness over long periods. Recent research efforts have been directed toward developing chemical controlled release devices which result in effective control over long periods but avoid or limit human health and environmental concerns.
Two basic requirements are imposed on development of such chemical controlled release systems. First, the active chemical must be environmentally safe and acceptable. Accordingly, the actiVe chemical must have a reasonably short half-life, exhibit little soil mobility and cause the desired effect only in the prescribed zone. This criteria requires a device and/or method Which delivers the active chemical at a controlled delivery rate and in a prescribed zone. Further, the cost of replacement must be minimized. This criteria requires a system that remains active for extended period of time (10-100 years).
The technology which has been developed to meet these two requirements is implemented by devices that are known as chemical controlled release devices. These devices are based on the principle of long-term controlled release of an active chemical from a polymeric delivery system.
For example, such systems are disclosed in U.S. Pat. application Ser. Nos. 06/555,113, filed Nov. 23, 1983 which is a Continuation In Part of 06/314,809, and 06/314,810 both filed on Oct. 26, 1981; 07/086,757, filed Aug. 18, 1987, 07/072,080 filed July 10, 1987; and 07/091,918 filed Sept. 1, 1987 the contents of these applications being incorporated herein by reference. Such controlled release systems act as a reservoir for the pure active chemical, protecting it from photochemical, chemical, and biological degradation. In addition, the system provides a method for controlled release of the chemical into the surrounding environment. The chemical released into the environment surrounding the device establishes an effective zone of action. Thus, the polymeric delivery system maintains an effective dose of the active chemical for a substantial length of time in a zone surrounding the device. These systems provide advantages over single application methods Which typically result in higher than necessary concentrations immediately after treatment which subsequently degrade to a level beloW the minimum effective dose.
As an example, ongoing research has resulted in the development of a series of sustained release, polymeric delivery systems using trifluralin as a root growth inhibiting chemical. These devices were developed for protecting below ground burial sites from plant root penetration for periods from 75-100 years, as discussed by Cline et al. in "Long-Term Biobarriers to Plant and Animal Intrusions of Uranium Tailings," PNL 4340, Pacific Northwest Laboratory, Richland, Wash., 1982.
Recently proposed systems include a fabric, such as spunbonded polypropylene, with sustained release devices thermally applied to the base fabric. Such a device would control unwanted vegetation growth for periods of 10-100 years. These devices are more fully described in U.S. Pat. application Ser. Nos. 06/555,113, 07/072,080, 07/091,918 and 07/086,757 which are referred to above. It is envisioned that these devices may find several types of industrial and commercial applications, in addition to protection of nuclear and chemical waste disposal sites, where control of plant growth and intrusion is of primary concern.
Various geometric configurations and methods for producing these controlled release devices have been developed. For example, one process involves injection molding of hemispherical pellets directly to spun-bound geotextile fabric, as disclosed in U.S. Pat. application Ser. No. 07/086,757. Other variations in this basic method may include variations in the specific geometric configuration of the controlled release device nodules on the fabric, Variation in the concentration of the inhibition chemical in the controlled release devices, variations in the matrix of these controlled release nodules such as type of polymer or carrier used, and Variations in the type of active chemical. For example, suitable polymers include polyethylene, polypropylene, polyvinyl acetate, polyurethane, poly-vinyl chloride, ethylene propylene rubber, polyester, thermoplastic elastomer, and silicon rubber. In addition, the formulation of the controlled release devices may have a Wide variation. One example includes a controlled release device which consists of 68% powdered polyethylene (USI Microthene 710-20), 18% carbon black (Monarch 1100 from the Cabot Corporation) and 24% trifluralin (available as Treflan). As will be recognized by those skilled in the art, many other variations and combinations of these and other materials are possible.
Additional potential geometric configurations include polymer containing gaskets as disclosed in U.S. Pat. application Ser. No. 06/555,113. Other configurations under consideration are webbing, tubes, and ropes containing the chemical controlled release system.
Because several potential configurations of the chemical controlled release device are possible depending on the type of control desired and the most advantageous method of application, a system is required as a tool to aid in the design of potential controlled release devices. This method or tool needs to be able to determine the performance characteristics of a proposed control device and to determine the optimal composition of a device to meet performance objectives in a specified environment.
As discussed in more detail below, the performance characteristics of a device are related to the release rate of the active chemical from the device. Therefore, the system must have the ability to predict the effect of the shape of the device and the composition of the device (i.e., type and percentage of polymer, concentration of active chemical, and the type and percent of carrier) on the release rate.
Two aspects of the release rate are particularly relevant to the controlled release device design and application. First, the device must be able to release the active chemical at a predictable, controlled rate that is effective in causing the desired effect. Second, the device must be able to limit the release rate to the minimal required values, thus extending the useful life of the device by not depleting the reservoir of active chemical in the device unnecessarily.
In addition, the designer of the specific controlled release device requires a tool for determining the effect that different system characteristics, including characteristics of the media into which the chemical will be released and device characteristics, will have on the effectiveness and lifetime of the proposed device under different conditions. For example, a system user may need to determine the optimal release rate to ensure a certain effective lifetime of a controlled release device. In another situation the system user may want to determine the effect that changes in the shape, size or composition of the controlled release device will have on the release rate and the effective zone and lifetime of the device. The user may also need to determine the effect of the media characteristics or the compositional characteristics of the device on effectiveness and lifetime.
Therefore, in view of the above it is the primary object of the present invention to provide a knowledge system that can be used as an engineering design tool for chemical controlled release devices.
It is a more specific object of the present invention to proVide a system for simulating the effective zone around a controlled release device.
It is a further specific object of the present invention to provide a system for simulating the effective lifetime of a controlled release device.
It is a further specific object of the present invention to provide a system for evaluating the environmental performance of controlled release devices with specified parameters in causing the desired effect either totally or with some degree of selectivity.
It is still a further specific object of the present invention to provide a system for determining the compatibility of polymers, carriers and active chemicals in providing a controlled release device with the desired performance characteristics.